Hello.

1) Just got 91 Accord LX with 190,000 miles for my son's first car (and my first time owning/working with a Honda.) Fortunately I drove it for a day and discovered Brakes issue by bumping a car parking in a lot when brakes failed. They seemed to be working fine then pedal started to really sink and braking was very slow to happen.

2) Symptoms: Zero noise in the pads (screeching), zero brake warning lights of any kind on, the reservoir is completely full of brake fluid, I do not see an ABS reservoir. When i press the brakes with car on, I can hear a hissing sound like air going out or a tire from left of the steering wheel and brake pedal slowly sinks to floor, the car idles higher. When I release the brake pedal, the idle returns to lower. I hear a clicking noise when in driver's seat to do the tests I found in this thread https://honda-tech.com/forums/honda-...ssure-3338859/ It is very clear loud click, click with each light press of the pedal with the engine off. I will put the results of the suggested tests in the thread below in red ink.

THANKS in advance very much for any suggestions.

From the thread:
"This information is from my service manual under BRAKE BOOSTER INSPECTION:

Functional Test
1. With the engine stopped, depress the brake pedal
several times, then depress the pedal hard and hold
that pressure for 15 seconds. If the pedal sinks, the
master cylinder, brake line or a brake caliper is
faulty. There is a very small amount of sink after the 15 seconds. I was hoping for a very detectable sink and just replace the master cylinder, but it was not super clear as it only slightly sinks.

2. Start the engine with the pedal depressed. If the pedal
sinks slightly, the vacuum booster is working. If
the pedal height does not vary, the booster or check
valve is faulty. Yes there was a slight sinking upon starting the engine indicating booster okay. This was confusing as other tests indicated not okay. For this, there was a definite sinking upon start.

Leak Test
1. Depress the brake pedal with the engine running,
then stop the engine. If the pedal height does not
vary while depressed for 30 seconds, the vacuum
booster is OK. If the pedal rises, the booster is faulty. This test however indicated faulty as there was a definite rise in pedal after turning the engine off. So first test said good, this one indicated bad. But the pedal is not rock hard at all. It sinks to the floor with the hissing sound and idles higher when engine on.
CAUTION: Do not try to disassemble the booster.
Replace the booster assembly with a hew one.

2. With the engine stopped, depress the brake pedal
several times using normal pressure. When the pedal
is first depressed, it should be low. On consecutive
applications, pedal height should gradually rise.
If the pedal position does not vary, check the booster
check valve. There was a gradual rise in pedal height on this test indicating booster okay again.

Check Valve Test
1. Disconnect the brake booster vacuum hose at the
booster.
2. Start the engine and let it idle. There should be vacuum
available. If no vacuum is available, the check
valve is not working correctly. How How do I check "should be vacuum available"? I read a post about trying to blow into it, but is there a better way to test?
Replace the check valve and retest."

Thanks again for any help with finding which part of the brake system could be trouble here.

 

You would check for vacuum at the brake booster hose by covering the open end of the disconnected hose with your thumb or something. When the engine is running, you should feel that hose sucking your thumb against the hose. Pull your thumb away and it should suck a lot of air into the hose & make some noise.

The rest of the results are a little confusing like you noticed. It might be the vacuum booster is bad; but instead (i'm not completely sure about this...) it might be that the brake pedal height adjustment is messed up. The booster and the MC don't always get along well with someone who likes to "personalize" that adjustment.

 

I take the hose off of the engine intake manifold side, correct? So it stays on the booster, off the other side and test with thumb is my plan tomorrow.

Also- I did a test drive today and noticed the hissing sound is happening at all times when the brakes are depressed. It never stops making the hissing sound. Don't know if that helps make the confusing/mixed symptoms lean in one direction more. I also noticed the increased idle was only when the car was in park. When it is in gear, the idle did not go high. As I think now, it may have actually decreased at a stop light when I was pressing the brake pedal with two feet.

If it is brake pedal height, is adjustment of that able a big job or pretty straight forward? Thank you very much.

 

I reread directions in my original post and see it said there "1. Disconnect the brake booster vacuum hose at the
booster. " SO I had that backwards. I was mixing it up with instructions in this article https://itstillruns.com/test-brake-b...e-7502988.html.

When I did what that article said, the valve tested fine. I could not blow air in when I tried and it did come through if I sucked. I read that valve can be cleaned with PB blaster to make it work better.

What did happen when I removed it was the idle started revving up and down all by itself. With no hose on the intake manifold, the idle went up and down as if I were pressing on the gas the entire time it was on. There was no pressure at all on the hose which I think is right, because the vacuum comes from the other direction. I need to take the hose off the booster and see what happens then. Tomorrow. So far with first reverse test, the valve seems fine. Not sure what the revving up and down means with the brake booster hose off of the intake manifold.. Any ideas?

 

What's supposed to happen, is if you take the hose off the booster, you should feel the engine vacuum the way I described. And since it's sucking air in through that hose the engine RPM will race as if you stepped on the accelerator pedal. Same thing if you take the hose off the manifold, except you feel the vacuum on the hose-nipple of the manifold. So that's good.

Then with the engine off, you should be able to blow air towards the engine, but not suck air away from the engine. That part sounds like the check-valve is backwards, but check again because that all depends on which end is disconnected.

The little plastic check-valve (#7) should have an arrow on it - pointed towards the engine.

 

Thank you very much for the diagram. I tested the valve again from the other side and there was air flow through in the proper direction. It wasn't super easy like a straw or a hose, pretty difficult to push air through. But it did go through on the test. I don't know if the post I read saying PB blaster can help improve the flow in the valve is true or if that is necessary.

I have decided now after consulting with a friend that it is very likely the booster. The pedal became increasingly hard until regardless of the minutiae of the tests confusing things, it seems pretty clear there is no booster functioning. I will do a search on booster for more, but if anyone sees this- is a booster pretty easy to replace? I have never done one and said friend who helped determine booster said I could probably do it. It is about four bolts and he said there is NO Bleeding of the system needed if I am just changing the booster out. I called a shop and they want $200 labor only to put it on. Ordered this part from Rock Auto for $99.78.
https://www.rockauto.com/en/moreinfo...=1167106&jsn=8.

Just looking for any experiences people have had to let me know if I would get in over my head on anything if I take a shot at it. As said this Honda is new to me and the only Honda I ever had/will work on. I have done basic repair like thermostat on an 86 Ford F150, oil changes, gasket replacement on a 92 toyota Previa, a radiator replacement, spark plug replacements. Small things like that. I don't have $200 for labor, so would like to try it if it's as easy as he said. This diagram seems like it can help.
Thanks again and thanks in advance for any tips/things learned from anyone who has swapped out a booster.

 

I haven't done it, but like you can see it's only a handful of bolts.

The real trick is adjusting the length of the pushrod through the middle of the booster. Honda calls out some special tools, more like measuring fixtures that you use for that. The procedure is kinda involved, and especially important if there's any suspicion that it's been adjusted improperly for personal preference. If you mis-adjust one thing and try to compensate by mis-adjusting something else, pretty soon the whole system won't work properly. It's in the Helm shop manual and it looks easy to do with the "special" measuring fixture - although it also looks like it can be done by measuring & adjusting after you understand the procedure.

When you begin pressing on the pedal, the booster needs to begin opening a vent to let air in & help push against the master cylinder. If the pushrod at the pedal is wrong that won't begin happening at the right spot. The master cylinder also has a fluid vent that allows the whole brake system to depressurize and release the brakes. If that isn't open when you're not pressing the brake pedal, then a temperature change at the wheels can lock your brakes.

So if your brake system is properly set up to begin with, and it's just a blown booster, you're in luck. You need to compare the adjustment length of that shaft new vs. old, and make sure they're the same. If they're not, then you should be suspicious that the adjustment was messed up to begin with, and you'll have to do that whole process. That's probably what the shop is estimating for.

 

I don't see why not. The biggest issue is having to work under the cramped dash.
Jim, is the set up tool something you can fake with a piece of metal or stiff cardboard? Just wondering, as he'll more than likely be under the dark dash with hardly any light to see with (if it's anything like my Accord). A "pre-set" fixture tool would simplify the job, even if it takes time to make the setting tool.

 

IIRC from changing the MC in my 95 Integra, you use the tool in the engine compartment before you bolt the MC up to the booster. For me, I was installing a new MC on a car that I was the only owner, so I wasn't concerned with the pedal pushrod being adjusted wrong.

I think with the MC removed, you put the tool up against the MC & adjust the tool so it just comes up against the piston rod. Then you take the gauge tool out & bolt it up to the booster, where the MC will mount.

The gauge tool is used to set the adjustment of the push rod under the dash. You adjust the pushrod length under the dash, but then you check your adjustment at the gauge tool in the engine compartment. When it's correct, you remove the gauge tool & install the master cylinder.

The only reason I'm talking about this is my suspicion that part of the problem here might be misadjusted pushrod to begin with. Otherwise you could simply measure the pushrod sticking out from the old booster before you take it off. Then adjust the new one to the same measurement.

 

Here's a brake tool that you'd use on some Chevys. I only show it here because it's more obvious how it works.



Honda's tool looks like this when it's put up against the master cylinder.


And... I'm not sure if that part number is the same for any & all Hondas? Or if there's different ones with different size or shape depending on which Honda.